Earth 295: Age of Apocalypse 

  
Located in Apocalypse´s citadel where once was New York City, this breeding pens served as concentration camp and genetic experiments core,  where people are imprisoned, tortured, and experimented on by the Dark Beast . Ruled by Sinister and administer by Dark Beast, this treachous place was the prison for years of many mutants. Using the brains of six powerful telepaths, the gate keepers, they sedated all prisoners to avoid any attempt of escape. 
 
Moreover, the Elite Mutant Force is tasked with maintaining control of Apocalypse's breeding pens. I n this breeding pens, Beast intent on breeding more powerful mutants according to Apocalypse  desires. However, while Sinister was methodical and rational in his experiments, McCoy (as ruthless as his mentor) sadistically delighted in causing pain to his lab subjects and in the cruelty of his experiments, which is why he was nicknamed the Beast.  McCoy also experimented on himself in order to further his mutation, and gained his ape-like bestial appearance. Any mutant that he deemed unworthy was turned into a component of a genetic stew that was used to create Apocalypse's army of Infinites . Despite Apocalypse had signed the Kelly Pact that regulated experiments on living beings, McCoy still doing his evil experiments.         
 
For years, Cyclops one of the most trusted Prelates, helped people to escape from the pens, notably Polaris, X-Man and Jean Grey. At the end of Age of Apocalypse, he joined forces with Jean Grey and they lead the final riot of the pens and liberated the prisoners. In order to achived their plans they destroyed the Gate Keepers and shut down the electricity supply.
 
Notable Prisoners: Blink, Artemis, Avalanche, Blob, Newt, Phantazia, Polaris, Pyro, Jean Grey, Christopher Summers, Power Pack, Wolfsbane, Jamie Madrox, Karma, Scarlett, Kirika.  
 

Years later, after the defeat of Apocalypse, the breeding pens became "The pens: National monument historic landmark 7148", a museum kept as a warning from history and honor those who died there. When, the Timebroker sent the Exiles to Age of Apocalypse, they arrived to this universe at the museum where they had an encounter with his former enemy Holocaust and supposedly they became teammates.
 

Other media  

Video games 
 
X-Men Legends II: Rise of Apocalypse 
 

In this RPG, the breeding pens appears in ACT 4 inside Apocalypse´s tower. As in comics, the breeding pens are the genetic pool of Sinister´s experiments. The brain trust act as sedative to prisoners as well. The mutant team must destroy  all of the brains and battle Stryfe.